This invention relates to tape guides for use, in a pair, in a magnetic tape cassette.
Conventional magnetic tape cassettes use a pair of tape guides to guide the tape in its travel. For example, FIG. 1 shows, as exploded, a video tape cassette of the VHS format. The cassette comprises an upper housing half a, a front lid b pivotally connected to the both ends of the front side of the upper housing half, a pair of reels c on which a length of magnetic tape is wound, and a lower housing half d, with a pair of tape guides e located at both corners of the front side of the lower housing half d. When the magnetic tape is played back, it runs in sliding contact with the tape guides e. To ensure smooth running of the tape, the tape guides must be of a material having sufficiently high surface precision, dimensional stability, low rate of abrasion, and high slipperiness. Heretofore most tape guides have been made from metals such as SUS grade stainless steels and hard chromium-plated brass that can meet these qualitative requirements.
However, the metallic tape guides have the disadvantages of low productivity and high cost because their manufacture involves many steps including stock forming, grinding, plating, finish polishing, and inspection.
It has been proposed to replace metals for tape guides by acetal plastic (POM) or ultra-high-molecular-weight polyolefin, with or without lubricant, wear-resistant pigment, etc. The use of these substitutes has, however, been limited because of their high material prices and rather inadequate properties. For example, Japanese Patent Application Kokai No. 1-292045 teaches fabrication from an ultra-high-molecular-weight polyethylene or polypropylene having a molecular weight of half a million to one million or their copolymer in which an anisotropic inorganic substance, e.g., inorganic particles in the form of whiskers or rods such as glass fiber, or planar inorganic particles, e.g., of graphite or molybdenum disulfide, is dispersed. However, POM has low wear and other properties yet to be improved and is, moreover, too expensive. Ultra-high-molecular-weight polyolefins have desirable properties but have shortcomings of poor moldability and costliness.
Other problems common to the guide members made from the polyacetal and ultra-high-molecular-weight resins are adsorption of ambient dirt and dust or tape sticking by dint of static charge caused by friction.
As stated above, the manufacture of metallic tape guides that involves many steps such as stock forming, grinding, plating, finish polishing, and inspection have the disadvantages of low productivity and high cost. POM and ultra-high-molecular-weight polyolefins are inferior in abrasion wear and moldability and, moreover, are costly.
The present invention is aimed at providing tape guides for tape cassettes which eliminate the disadvantages of the prior art and exhibit performance as tape guides comparable to those of metals, the guides being able to be made from low cost material, with good moldability, and at low manufacturing cost.